Teriyaki Chicken Fillet Sandwich (Homemade Teriyaki Burger with Sandwich Bread)

Prep the chicken. Thoroughly wipe off any drip and blood spots with paper towels, as they cause off-flavors, and use a knife to remove tough cartilage, sinew, and blood spots that would be unpleasant to eat. If any feathers remain on the skin, pull them out by hand.

Place the chicken in a food-safe plastic bag, add the soy sauce, and massage it in well so it coats the chicken all over. Press out the air and tie the bag tightly closed.

Refrigerate skin side down, ideally marinating for half a day or more. If you're short on time, about 30 minutes will do.

Transfer the marinated chicken to a heatproof container, squeezing the bag well to add any remaining soy sauce. Place it skin side up and stretch the skin over the meat to wrap it as you shape the piece.

Set the heatproof container in a frying pan and pour in water to about halfway up the side of the container so it won't boil dry during cooking. Turn on the heat and bring to a boil, then lower to low heat, cover, and steam in the water bath for about 20 minutes.

While the chicken steams, make the toast. Put butter in a frying pan and add a little vegetable oil so it's less likely to burn, then heat. Once the butter melts, add a slice of bread and toast one side only until evenly golden, pressing lightly with a spatula. Toast the second slice on one side the same way, then wipe any crumbs or burnt bits from the pan with a paper towel.

When the time is up, check that the chicken is cooked through. Aim for a core temperature of 75°C held for at least 1 minute. If you don't have a thermometer, cut into the thickest part with a knife and be sure to check that it's white all the way to the center with no raw-looking spots left.

Remove just the chicken and transfer the steaming juices left in the container, infused with the chicken's savoriness, to the frying pan. Add the sugar, turn on the heat, and reduce lightly.

Once it comes to a boil, return the chicken and coat it all over with the teriyaki sauce. Finish by reducing the sauce alone until it thickens.

Wash the lettuce and pat it thoroughly dry. Spread mustard on the untoasted side of the bread, if desired.

Place the teriyaki chicken on the toast, top with lettuce, and add plenty of mayonnaise. Set aside any leftover sauce.

Top with the second slice of bread and press down firmly from above so the fillings stick together and the sandwich holds as one. Cut it in half to finish.